No, that's a terrible idea. In every other creative enterprise the artist is paid to produce a work. They are effectively selling a license to a company granting permission to use and promote the work.. any situation where an artist has to pay for the privilege of a company using their creations is predatory and unethical.
The feedback process doesn't change this, in general when a company is seeking a specific creation they draw it up as a list of requirements that must be met before any payment is given to the artist.
If UGC wants more money they have to do what every other sports enterprise does: bring in advertisers, attract sponsors, and sell tickets.
Redrum approached me about this as well, and I have to disagree (somewhat).
To be blunt, if the expectation is that any mapper who relies upon competitive communities for feedback is expected to pay money out of their own pocket to the comp communities to fund prize pools, then yah, thats not great. Even though I made a pretty good chunk from Valve, it really didn't last very long, and I'm pretty broke right now compared with pretty much anyone else who has a real job.
But, thats not really the sort of model that Redrum is talking about (Edit: I guess the above may actually be his expectation, if so I disagree with it). Basically, we should be looking more at the model from the item workshop, which allows creators to choose mentors/feedback providers/tool makers and so forth and valve compensates them out of their own pocket (they get a cut of valve's half of the item/key cost). So Valve pays the feedback source, the item maker gets their cut without any missing, and everyone is rewarded for the work they put in.
See the following for more info:
http://steamcommunity.com/games/SteamWorkshop/announcements/detail/1819734886367365945 The primary issue of course, is that valve doesn't get a cut of stamps. The money goes 100% (minus taxes) to the map maker, where with items valve gets 50% (?).
I definitely think that feedback is essential to make anything good, and if Valve wants to provide money to groups to incentivise feedback, by all means! Why shouldn't they? But, I don't think any mapper will be well off enough in the immediate future to really take a cut from their payout.
I also disagree with the "advertisers, sponsors, tickets" bit. While something like that might be reasonable, in the end I see no reason why a part of the pie shouldn't be going to competitive communities as well, and to be honest, I don't think comp players are in a position where tickets/sponsors are going to be a valid or reliable way of maintaining prize pools. Or, to put it another way, ESEA already sells tickets, but they sell them to the players who play in the league, and that's where the prize pool comes from. And, while not a terrible system, its certainly not breaking bank for anyone involved (other than ESEA).